Our Sages teach that when the Messiah arrives the festivals will cease to be observed, but Purim will continue to be observed. The Midrash (Mishlei 9) derives this unusual conclusion from a statement in Megillat Esther, (9:28) “the memory of Purim will never cease from among their descendants.”

The commandments written in the Torah (which include all of the holidays) will never cease to be observed, even when Messiah comes, as it says in the Torah itself referring to its commands, "it shall be observed throughout all generations." [Note my usage of "shall" and not "will."] So based on this the holidays will always be observed. Period.
– ezraOct 21 '16 at 3:47